In large scale computing and data storage systems, one issue that arises is where to store data. Different types of data storage may have different costs or retrieval speeds. When storage devices are geographically distant from the source or consumer of the data, there may be issues concerning the availability of bandwidth to transmit the data to these distant locations. When there are many storage devices available, there may be issues of balancing usage across the various devices to avoid placing an excessive load on any one device.
Additionally, regulatory issues and commercial expectations may affect where and how data is stored. These regulatory or commercial factors may govern how many copies of the data are to be stored, what type of security is to be applied to the data, where (geographically) the data may be stored, how fast the storage facility is expected to respond to retrieval requests, or any other aspect of data storage. For example, the manner in which medical records are stored is often governed by national laws. Such laws may specify that a certain type of encryption is to be used to protect the data, and that a certain number of copies of the data are to be kept.